Why no shadow projection on the plane for this png ?

[ThomasCartier]

Hi,
My png doesn't have any projection on the ground.
It is visible, but the spot above it doesn't project the shadow on the plane beneath.
Is it normal ?

pub fn environment_map_setup(mut commands: Commands, mut meshes: ResMut<Assets<Mesh>>, asset_server: Res<AssetServer>, mut materials: ResMut<Assets<StandardMaterial>>) {

        let texture_handle = asset_server.load("sl5.png");

        let aspect = 0.25;

        // create a new quad mesh. this is what we will apply the texture to
        let quad_width = 15.0;

        let quad_handle = meshes.add(Rectangle::new(quad_width, quad_width * aspect));

        // this material renders the texture normally
        let material_handle = materials.add(StandardMaterial {
                base_color_texture: Some(texture_handle.clone()),
                alpha_mode: AlphaMode::Multiply,
                unlit: true,
                double_sided: true,
                occlusion_texture: Some(texture_handle.clone()),
                ..default()
        });

        commands.spawn(PbrBundle {
                mesh: quad_handle.clone(),
                material: material_handle,
                transform: Transform::from_xyz(0., 1.5, 0.).with_rotation(Quat::from_rotation_x(-90.0_f32.to_radians())),
                ..default()
        });

        commands.spawn(SpotLightBundle {
                transform: Transform::from_xyz(0., 4.0, 0.).looking_at(Vec3::new(0.0, 0.0, 0.), Vec3::Y),
                spot_light: SpotLight {
                        intensity: 400_000.0, // lumens
                        color: Color::WHITE,
                        shadows_enabled: true,
                        inner_angle: PI / 4.0 * 0.85,
                        outer_angle: PI / 4.0,
                        ..Default::default()
                },
                ..default()
        });
}

The spotlight is above the png, looking at the ground.
It should project the image of the png on the ground plane.

The original png:

Instead, it doesn't. Please see the picture:

No shadow beneath the image, but the quad is blocking the light from the spotlight (the white at the very bottom).
Instead, we should have the projection of the three black bars of the png image.
Meaning the actual image has no importance on the shape of the shadow. Only the mesh ?

How do we deal with that situation ?

Thanks

Update: another pic, to make it clearer:

The shadow beneath has the shape of the quad, not respecting the drawing alpha of the image on it.

[ThomasCartier]

Ok it works with Alphamode "Blend". Stupid me.
Closing!